strlen() not working with string variable

c++ c++11 strlen

12,064

strlen is a function from C and works with C strings (char *).

For proper C++ std::strings use the .length() or .size() member functions.

In fact most standard headers that start with 'c' include functions that C++ inherited from C. In your case you most likely don't have any reason to use <cstring> if you're already working with C++ strings.

12,064

Waters Sharma

BY DAY : I am currently intern at classic tech working in web development department. In code Ignitor framework. IN the Morning :I am also a BSc.C.S.I.T student . AND Night I am working on some projects in JAVA

Updated on July 10, 2022

Comments

Waters Sharma almost 2 years
```
#include <iostream>
#include <string>
#include <cstring>


using namespace std;

int main()
{
    string b="hello";

    cout<<b;

    int c = strlen(b);

    cout << "Hello world!" <<c<< endl;
    return 0;
}
```
When I try to run this I get the error below
```
||=== Build: Debug in strlen (compiler: GNU GCC Compiler) ===|
C:\Users\Waters\Desktop\hellow world\strlen\main.cpp||In function 'int main()':|
C:\Users\Waters\Desktop\hellow world\strlen\main.cpp|14|error: cannot convert 'std::string {aka std::basic_string<char>}' to 'const char*' for argument '1' to 'size_t strlen(const char*)'|
||=== Build failed: 1 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|
```
- dgsomerton almost 8 years
  
  try strlen(b.c_str())
- dgsomerton almost 8 years
  
  even better: try c = b.length()
- Nick Matteo almost 8 years
  
  @WatersSharma: because strlen takes a char * argument, not an std::string, which is totally meaningless to it. std::string::c_str() is a function returning a C string (const char *).
- dgsomerton almost 8 years
  
  @WatersSharma: if you bothered to read the error message, it says right there: cannot convert 'std::string {aka std::basic_string}' to 'const char*' for argument '1' to 'size_t strlen(const char*)'
- molbdnilo almost 8 years
  
  Whatever source you're learning from, throw it out and get a decent book.
- Zulan almost 8 years
  
  See stackoverflow.com/a/388282/620382
cwschmidt almost 8 years

You surely meant, C strings must be terminated by '\0' not by '\n'.
Peregrin almost 8 years

@cwschmidt aha, you are damn right :D I should probably get some sleep
coyotte508 almost 8 years

also const char *b instead of char *b.
Peregrin almost 8 years

@cwschmidt well, in the example string isn't const
cwschmidt almost 8 years

@Peregrin What do you refer to? It's irrelevant if it's const or not, C strings have to be terminated by '\0'